Current techniques for the detection of chromosome abnormalities are time consuming and require cell culture and preparation of metaphase chromosome. Interphase cytogenetics using in situ hybridization of fluorescent labeled DNa probes is potentially rapid, relatively inexpensive, and lends itself to automation. 90+% of all live born chromosomal abnormalities consist of trisomy 21, 18, 13 and numerical abnormalities of X and Y. It is the goal of this research to generate single copy chromosome-specific DNa probes suitable for detection of numerical abnormalities of chromosomes 21, 18, 13, X and Y. Each probe set will consist of at least 20 kb of unique DNA per desired chromosomal band. Probe sets that pass preliminary evaluation will be tested as a diagnostic reagent in a blind clinical trial, with the ultimate goal of offering a rapid, semi-automated trisomy + X and Y screen as a diagnostic service in a clinical laboratory. Eventually probes suitable for detection of translocations, deletions, and a full karyotype should also be generated.